Pseudoaneurysm at M3 of the middle cerebral artery: Morphological changes on serial radiological examinations

Abstract

A 20-year-old man presented with consciousness disturbance and hemiparesis, and computed tomography demonstrated subarachnoid and intracerebral hemorrhage. Angiography on admission demonstrated a slight irregularity of the middle cerebral artery (MCA) branch. Angiography on the 12th day showed a suspicious lesion at M3 of the left MCA. Angiography performed 24 days after the onset disclosed an aneurysm at M3. The aneurysm was trapped and resected after superficial temporal artery-MCA bypass. Pathological examinations revealed that this distal aneurysm was a pseudoaneurysm without vascular components in its dome. Although a lesion that may cause subarachnoid or intracerebral hemorrhage was not detected on the initial angiography, repeated examinations revealed the atypical vascular lesion in distal MCA.

Introduction

Distal middle cerebral artery (MCA) aneurysms are not common, constituting only 4%–5% of all MCA aneurysms.^1,2 Further, dissecting aneurysms or pseudoaneurysms of the distal MCA are extremely rare.³ Dissection of an artery is caused by trauma, vasculitis, atherosclerosis, neoplastic embolus, and bacterial infection.³ There have been only six reported cases of spontaneous dissecting aneurysms of the M3 or more distal locations.^2–7 On the other hand, most pseudoaneurysms result from head injury or infection.⁸ Some reports have described pseudoaneurysm formation on the distal MCA.^8,9 We encountered a patient with an aneurysm at M3 of the MCA. In our case, the initial radiological examinations failed to demonstrate a definitive aneurysmal lesion. After 24 days, the aneurysm was demonstrated on angiography. The aneurysm was resected after superficial temporal artery (STA)-MCA bypass. In this report, we discuss the radiological and pathological findings, and the management of a rare M3 pseudoaneurysm.

Case presentation

A 20-year-old man without a significant medical history suddenly showed consciousness disturbance, convulsion, and vomiting while he was drinking alcohol. He presented with consciousness disturbance and right hemiparesis on admission. He had no fever, and blood examinations revealed no abnormality, including infectious signs. He also had no experience of head injury. Computed tomography (CT) revealed subarachnoid hemorrhage (SAH) and an intracerebral hematoma in the left temporal lobe (Figure 1(a)). CT angiography (CTA) showed no abnormality in cerebral arteries (Figure 1(a)). Angiography on admission failed to demonstrate an aneurysm, but a slightly irregular arterial wall of the MCA was observed (Figure 1(b)). Angiography on the 12th day showed a suspicious lesion at the M3 segment of the left MCA (Figure 1(c)). Angiography performed 24 days after onset showed an aneurysm at the left M3 (Figure 1(d)). On the 25th day, STA-MCA bypass followed by aneurysm resection was performed. The MCA distal to the aneurysm was transiently occluded with forceps and the M4 branch to be anastomosed was selected using micro-Doppler ultrasonography. STA-MCA bypass was carried out and the patency of the bypass was confirmed with micro-Doppler ultrasonography. Then, the aneurysm was resected after trapping of the MCA. Postoperative angiography showed the disappearance of the aneurysm and patency of the bypass (Figure 1(e)). Pathological examinations of the lesion demonstrated wide disruption of the internal elastic laminae, intimal thickening, and collagen fiber deposition in the media (Figure 1(f)). No bacterial or fungal infection was detected. There were no true vascular components in the aneurysm dome. These findings were consistent with a pseudoaneurysm. He was transferred to another hospital for rehabilitation on the 39th day with left hemiparesis and motor aphasia.

Figure 1.

(a) CT on admission showing SAH and intracerebral hemorrhage (left panel). CTA showing no vascular lesion (right panel). (b) The initial angiography showing slight wall irregularity of the distal MCA (arrow). (c) Angiography on the 12th day showing a suspicious bulging on M3 of the left MCA (arrow). (d) Angiography on the 24th day showing an aneurysmal lesion at M3 (arrow). (e) Postoperative angiography showing the disappearance of the aneurysm and patency of the bypass. Arrows indicating the distal MCA to the resected lesion. The MCA distal to the lesion is fed by the STA. (f) Microphotograph of the specimen demonstrating granulation, disruption of the internal elastic laminae (arrows), and thickening of the intima (asterisk). Elastica van Gieson stain, original magnification: ×20. CT: computed tomography; SAH: subarachnoid hemorrhage; CTA: computed tomography angiography; MCA; middle cerebral artery; STA: superficial temporal artery.

Discussion

Pseudoaneurysm can result from trauma, mycotic infection, vessel dissection, and congenital collagen deficiency.¹⁰ Pseudoaneurysm cavity formation in a hematoma or thrombus located at the rupture site of a cerebral aneurysm has been reported.^10–12 Pseudoaneurysm is characterized by the presence of an organized hematoma and fibrosis outside the true lumen, instead of true vascular structures.⁹ There have been some reports describing cases of pseudoaneurysms in the distal MCA. Among them, some patients had no history of head injury or infection.^8,9 Our patient also had no history of head injury or infection, and the etiology of the lesion remains unknown.

Gripp et al.¹³ reported a case of pseudoaneurysm originating from a dissecting distal MCA. Dissecting aneurysm might be a cause of pseudoaneurysm formation. There was a report describing a dissecting MCA aneurysm patient presenting with morphological changes on radiological examinations.^3,14 In our case, there is a possibility that a small dissection or laceration initially occurred in the fragile portion of the distal MCA branch, and resulted in hemorrhage. After a period of time, dissection progressed, or a pseudocavity was formed in the intracerebral hematoma. These progressions might be detected as morphological changes on radiological examinations.

As for radiological findings, angiographical findings changed during 24 days after onset in our case. These changes in radiological examinations might be due to thrombosis and recanalization of the lumen formed in the dissected cavity or hematoma, progression of the dissection, or pseudoaneurysm formation. Radiological findings might change over time, especially in cases of distal cerebral artery aneurysm. Among six reported cases with distal MCA dissecting aneurysms, two cases showed morphological changes in about two months.^4,5 In these cases, initial angiography showed a small aneurysm or no lesion. One of them showed similar pathological findings as ours suggesting formation of a pseudoaneurysm.⁵ The formation and enlargement of a pseudocavity adjacent to the aneurysm might occur in such cases. Indeed, in some reported cases of pseudoaneurysms, hematoma was formed in the brain, and hematoma was the main lesion rather than SAH.¹² Therefore, even if a vascular lesion that may cause SAH and intracerebral hemorrhage is not detected on the initial angiography, repeated examinations are necessary for cases of uncommon intracranial hemorrhage.

In our case, after detection of the lesion, the patient was treated with a combination of STA-MCA bypass, followed by trapping and resection of the lesion. For STA-MCA bypass, the distal portion of M4 was precisely selected using micro-Doppler ultrasonography, as previously reported.¹⁵ This treatment might be the best option for such a patient to preserve blood flow in the MCA distal to the lesion.

Concerning histological examinations, main pathological findings of previously reported dissecting distal MCA aneurysms are disruption of the internal elastic laminae, organized thrombus in the dissected false cavity, and neointimal or fibrocellular proliferation. These findings were also found in our case.^3–5 Our case might be a pseudoaneurysm originating from dissection. Previously reported pathological findings of pseudoaneurysms are a dense fibrous vascular wall with foci of old hemorrhage and chronic inflammatory cellular infiltration.^8,9 The pathological findings of ours were consistent with pseudoaneurysm of the distal cerebral artery.

Conclusions

An aneurysmal lesion of the distal M3 of the MCA is rare. In such a case, the lesion might be a pseudoaneurysm, and the morphology may change on radiological examinations. Therefore, close observation is necessary. STA-MCA bypass followed by trapping of the lesion might be the optimal treatment.

Funding

This work was partly supported by research funds to promote the hospital functions of Japan Organization of Occupational Health and Safety to M.N.

Conflict of interest

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.